hey guys this is crema glasha with AC suburbs tech and today what we're going over is how to explain superheat & sub cooling to your apprentice so what you need is an evaporator coil and an outdoor condensing unit and a gauge set I'm gonna cover sub cooling first and sub cooling is taken right here at the outdoor unit surface valve so it's the liquid line service valve it's the small one so some of the terms to remember that is that you have a red gauge red hose high side line liquid small tube okay so that's how you remember that so that's the sub cooling you're checking the sub cooling right there you're checking superheat over here so superheat is the vapor line and you're checking that with the blue gauge which is a low side with the blue hose and that is a vapor so the vapor line is always larger than the liquid line so you're checking total superheat out here and you're checking sub cooling right here so what is sub cooling sub cooling is the lowering and temperature of the liquid refrigerant in the condenser coil and we measure it where it comes out of the condenser coil over here so inside this outdoor unit you have a compressor and there's low pressure vapor coming into the compressor and high-pressure vapor coming out this high-pressure vapor is high temperature because of the because of the high pressure so what happens is the high pressure high temperature of vapor refrigerant starts traveling through this coil and this condensing units job is it's sucking the the air across this coil and then blowing the hot air at the top so what you're doing is you're rejecting heat from this high-pressure vapor refrigerant so as it's traveling through the the tubing within this coil it's lowering and temperature as a vapor and then it turns into a saturated refrigerant where you have vapor and liquid both exist at the same time once it gets to that point where you're saturated you're no longer lowering in temperature you're just phase changing from a vapor to a liquid so that would happen say in the center of this coil once it turns into a complete liquid say right about here then what's happening is it's then lowering in temperature as a liquid refrigerant so when you're measuring the pressure right here you're actually measuring the pressure in the saturated state right here so when you measure the pressure you're to convert that to saturated temperature as well you're going to take a temperature measurement on this liquid line and the temperature measurement is going to be the lower temperature after the refrigerant comes out of the saturated state I know that's hard to understand but you are measuring the pressure in the saturated state in the outdoor condenser coil but the temperature here is after the liquid lowers and temperature as it travels through the tubing and is rejecting heat to the outside air so that is sub courting the lowering and temperature of the liquid refrigerant now to measure sub coin what you do is you measure the pressure so say it's at 250 psi so this needle goes all the way up to say 250 and you bring the needle in to whatever refrigerant this is so this is an R 22 unit you can use this green pressure temperature chart that's overlaid on the gauge face so you bring it from the pressure into the green inner ring and that's when you read your saturated temperature this was an or for tonight unit you can take your your pressure and you bring it into the pink inner ring which is the saturated temperature at that pressure now if you don't have the the saturated temperatures overlaid on the gauge face then you can just use a PT chart if you have a digital gauge set it'll calculate automatically you just need to take your pressure reading and it will convert it to saturated temperature then you just take a digital temperature reading on the outside of this tube right here this liquid tube so the temperature on this liquid tube will be lower than the saturated temperature that you've you've converted the pressure to as an example if this unit was or for tonight and it said or for tonight on the outdoor unit reading plate and you measure the pressure on your liquid line of say 300 while this system was running and you brought that into a pink temperature of 94 degrees that would mean that the pressure converted the temperature of the saturated refrigerant is 94 degrees then you take an actual temperature measurement right here on the liquid line within a few inches of the port if you measured 84 degrees on the line right here that would mean that you have 94 degrees saturated temperature minus 84 degrees actual line temperature that's 10 degrees of subcode we use a sub coin measurement order to check the refrigerant charge level of an air conditioning system that has a thermostatic expansion valve so this is otherwise known as a te v or t --xv and it's a regulating metering device is actually able to open up the hole and close down the hole in order to regulate the refrigerant that's entering into this evaporator coil a dead giveaway that you have a TX v is a bulb like this or your external equalization line so if these are mounted outside of the coil then you'll know that you have a thermostatic expansion valve otherwise you may have to take this cover off in order to determine what type of metering device you have if you have a thermostatic expansion valve you want to get the sub coin measurement as close as possible to the target sub going reading on the rating plate so if there is no target sub calling rating out here it may be on the underside of the shroud so you may have to take the shroud off and look on the underside in order to determine what that target subcooling should be if you measure a higher subcooling then you have on the target sub corn then that means your overcharged if you have less sub corn then on here then your undercharged so if you had a target sub corn of 14 degrees and we measured 10 degrees then we would want to add refrigerant to this system in order to increase the sub point now if you didn't have a thermostatic expansion valve but you did have something that looked like this this is a fixed orifice metering device it's known as a capillary tube and these are also fixed offices as well so these are piston chambers and inside there is just a a fixed hole right on these right in the center here where the refrigerant travels through if you have a fixed orifice as the metering device at the evaporator coil then you need to check the refrigerant charge with the total superheat method when you're measuring the pressure on the large vapor line and taking a natural temperature reading on the line within a few inches of that port an example of measuring total superheat would be if you took a pressure reading on the large vapor line while the system was running and you measured about a hundred and twenty psi G on the outer ring if you brought that into the R for tonight saturated temperature and you converted that pressure it would be 41 degrees saturated temperature in the middle of the evaporator coil so then you're taking temperature reading with a digital temp meter on the large vapor line within a few inches of this port so if this temperature reading was say 54 degrees you take 54 degrees minus the saturated temperature of 41 degrees and you get 13 degrees of total superheat measured there is no rating on the outdoor unit rating plate or the indoor unit rating plate that tells you what the target superheat should be you should not set it at a certain pressure what you need to do is you need to take a indoor wet ball reading within the building so at the return you need to take a wet bulb reading with a digital psychrometer and then you take a outdoor temperature reading right near the outdoor condensing unit and you just take it out of the Sun and you don't get it near the the hot air coming out you put those two measurements on a super heat chart and you can determine what the target superheat needs the bit you can also use a target superheat app you can also use if you have a digital manifold you might be able to enter the the wet bulb temperature inside the building and the outdoor dry bulb temperature outside and and that may be able to come up with a target superheat for you we go into great detail with the target superheat in our book and also where to take your measurements at your indoor wet bulb and also your outdoor dry bulb so here's our book and we also have these quick reference cards that walk you through checking the charged with superheat and with sub cooling so also measuring delta T and the other cards have a PT chart and also refrigerant weights a troubleshooting guide and also when you walk up on a frozen evaporator coil what the steps are in order to determine what the problem is so just remember that target superheat with a system that has a fixed orphis is a moving number so just because you get a measurement of say 13 degrees of total superheat it doesn't mean that that's what the correct number should be if you measure their total superheat of 13 degrees and your target was 17 degrees and that means that your overcharged but if your target superheat was say 9 degrees and you measured 13 degrees then that means your undercharged I want to get back to what superheat actually is and superheat at the indoor evaporator coil sub coin occurs at the outdoor condenser coil but you have high pressure high temperature sub cooled liquid refrigerant travels from the outdoor unit to the indoor coil on the small liquid line so it enters the TXV as a high pressure high temperature sub cooled liquid refrigerant it then lowers the pressure at the metering device and when you lower pressure your lower temperature but what's happening is it travels through the refrigerant travels through the distributor tubes to the evaporator cool and it immediately changes to 80 percent liquid 20 percent flash gas so it's already in the saturated state when it enters the coil then the refrigerant is absorbing heat from the air crossing the coil and so it's not going to increase in temperature as it's absorbing the heat it's just gonna phase change so by the time it gets up to about here you're looking at a 50/50 mixture 50 percent liquid 50 percent gas by the time it gets up to here you're looking at maybe 80 percent vapor 20 percent liquid then it's getting up to about here and it's totally in the gaseous state the vapor State and then it can increase in temperature so the refrigerant is totally in vapor form at this point and then the increase in temperature as it's traveling through the tubes is called the superheat so between here and where it comes out of the evaporator coil right here is called the superheat and where the the vapor refrigerant travels to the outdoor unit that's called the total superheat by the time it gets out here I know it's hard to believe but we're measuring the pressure here too in order to measure the pressure of the saturated state in the middle of this evaporator coil we're doing that to convert it to saturated temperature so that's the only reason we're measuring pressure right here is to get a saturated temperature so if we know the saturated temperature right here on this coil when the temperature increases finally once it gets into the vapor state and it's increasing in temperatures as it's absorbing Heat the temperature measurement here is going to be higher than the saturated temperature measurement here and so in our case we use the example of 13 degrees increase of temperature so if this evaporator coil was running at a saturated temperature of 41 degrees but by the time the refrigerant came out on this vapor line it was 54 degrees and that mean it's 13 degrees of superheat and we're measuring over here which is the total superheat so we're picking up or reducing any temperature of the vapor refrigerant I'm it gets all the way out here so it should be very close our total superheat and our and our superheat should be very close within a maybe a degree or so unless these the vapor line is buried in the ground or something like that on the way to the outdoor unit so the beauty of the thermostatic expansion valve is it's gonna be able to hold the superheat at a steady amount because it's measuring the temperature on the vapor line and the pressure on the vapor line that's what we're doing that's what we're doing over here we're measuring the pressure and the temperature there's other components in the TXV such as the spring pressure but the whole point is that it's monitoring the superheat and it's adjusting the refrigerant flow to try to hold the superheat steady regardless of the heat load of the air coming across this evaporator coil so the whole point the whole reason that we don't check our total superheat that check the refrigerant charge of a system that has a thermostatic expansion valve is because this TSV is gonna try to hold the superheat study all the time as long as it has the correct amount of refrigerant entering the TX V so that's why when a system has at TX v we measure the sub cooling and that's going to tell us the refrigerant charge level if we don't have something that's like this the TX v that's able to hold the superheat steady then the superheat is going to fluctuate because you're only letting in the same amount of refrigerant all the time into this evaporator coil so that's why we have to measure the superheat the total superheat with our blue gauge on our vapor line in order to check the refrigerant charge of a system that has a fixed orphis I know that's a lot of information but that's what's actually happening in this system so we got to know what total superheat and the subcooling are in order to check the refrigerant charge and also to be able to quickly troubleshooting in it if it's not working properly we go into all the details in our book the refrigerant charging is service procedures for air conditioning I made sure that we had a large font size we've got pictures in order to determine what the problems are we have different scenarios the preparing a system full refrigerant with a vacuum and the recovery procedures all that tech stuff is in this book right here we also have a workbook for our book and this contains 1000 questions that I specifically want you to know so that you're an effective technician out there in the field and we're also providing our answer key and so we have the color images right here as well as all of our ABCD true and false questions so it's it's a lot of application questions and preparation of a system for refriger teching the charge troubleshooting and also air flow so we have that available as well so check this stuff out over at Amazon or over on our website at ICI service tech comm at our website we have a full outline of everything that's contained in this book hope you enjoyed yourself and we'll see you next time at EC service tech Channel